1. Field of the Invention
The present invention concerns a feed line for at least one local coil of a magnetic resonance tomography apparatus, of the type having at least one coil plug as well as at least one standing wave barrier to suppress unwanted radio-frequency currents on the conductor cable of the feed line.
2. Description of the Prior Art
For the implementation of measurements in the field of nuclear magnetic resonance tomography, radio-frequency coils in the form of local coils are used for the acquisition of alternating electromagnetic fields. To fulfill the need to optimize the signal-to-noise ratio, radio-frequency coils for different body regions of the patient to be examined are optimized with regard to geometry and their acquisition profile. An optimally close positioning of the local coils on the body of the patient enables a high value to be attained for the signal-to-noise ratio.
The local coils used in magnetic resonance tomography normally are designed as pure acquisition coils, with the spin excitation that causes emission of the magnetic resonance signals to be detected, ensuring with a whole-body resonator. A radio-frequency cable is necessary for transfer of the signal from coils to the acquisition system of the associated magnetic resonance system.
In the transmission mode of a measurement, the electromagnetic fields induce radio-frequency currents on the conductor shields of the cables of the feed lines for the local coils. These radio-frequency currents, known as standing waves can lead to image distortions or even to an injury to the patient. Standing wave barriers for suppression of these radio-frequency currents on the outer conductor of the cable accordingly are inserted into the feed lines of the local coils. The standing wave barriers (representing high-ohmic impedances) suppress the unwanted radio-frequency currents on the lines.
During data acquisition with the magnetic resonance system, the standing wave barriers rest on the patient. They must be maintained at a safe distance from the patient, which is why they are surrounded with a plastic housing. This leads to the situation that the standing wave barriers of the feed lines for the local coils exhibit a certain size and thus appear unwieldy and reduce the examination comfort for the patient.